Low-Voltage Cutoff Switch


A microcontroller-based voltage cutoff circuit, currently in use on several motorcycles. It is designed to monitor the voltage level for the battery, and activate an accessory circuit when the level is sufficiently high. If the level drops below a calibrated level, the accessories are cut off.

This circuit has 4 connections to the motorcycle:
* ground (from battery or chassis)
* battery +12V
* signal +12V (from the ignition circuit or a headlamp / tail light)
* switched +12V output from the relay

Accessories will be wired to the switched + ground connection.

The signal line provides "house" power, drives the microcontroller, and will be measured to determine whether to activate accessories. This line will draw very little current and will not be used to operate the relay (~ 160ma draw).

The relay will be driven from the +12V battery source, and will operate the switched +12V line.


MattH (Aug 28, 2014)
Note that you have to be able to program a Microcontroller IC for this project to be viable.
verdeva (Feb 16, 2014)
In the parts list an NPN transistor is listed, however the schematic uses a PNP transistor. Do show a revised schematic for this part, or is the parts list in error?